1. Field of the Invention
This invention relates to shock absorbing suspension systems particularly applicable to the front wheel of a bicycle.
2. Background of the Invention
This invention has particular application to bicycles that are referred to as mountain bikes or trail bikes and which are typically ridden over rough terrain. As is typical for all conventional bicycles, the front wheel of the bicycle is the steering wheel. Steering handles, i.e., handlebars, are interconnected to the wheel through a fork, the fork having parallel legs that extend upward from each side of the wheel axle and connect at the top of the wheel to a central steering tube that in turn is attached to the handlebars. The steering tube is rotatably mounted to the frame of the bicycle in a manner to support the frame on the wheel's axle while permitting rotation of the tube and thus turning of the front wheel relative to the frame.
Of concern to the off-road bicycle rider is the jolting of the front wheel as rocks and holes are encountered. This jolting is transferred to the rider through the fork, steering tube and steering handles. Besides the obvious punishment that is inflicted on the rider, there is the added concern for safety. A rider's steering handles are not so easily controlled at the instant of a severe jolt being experienced by the rider through the handles.
To accommodate this front wheel jolting, designers of trail and mountain bikes have developed front wheel, shock absorbing suspension systems.
Not previously mentioned but an important feature accommodated by the front wheel fork design is the brakes that are carried by the fork and which are applied against the front wheel rim to slow or stop the bicycle. The brake mechanism is mounted to the forks at the outer periphery of the wheel. Levers carrying a pair of brake shoes are manipulated by the rider via cables to simultaneously apply the brake shoes to both sides of the front wheel. The levers and brake shoes arrangement are designed and positioned for precise application of braking action against the wheel rim. The distance of the brake pads from the wheel axle has to be a constant distance.
Maintaining a constant distance is not a problem if the fork is a one-piece member. However, it is a problem that is encountered in designing a front wheel shock absorbing system.
Shock absorbing systems of the type contemplated herein and which have been successfully used to date have fork legs that include a rigid rod slidable in a rigid sleeve. A biasing member urges the fork's rods to an extended position relative to the fork sleeves. As bumps or holes are encountered by the front wheel, the biasing members collapse as the rods are forced into the sleeve, the biasing members largely absorbing the shock and rapid movement otherwise transferred to the steering handle.
Because the sleeves surround the rod at the wheel periphery, it has been considered necessary to attach the brake mechanism to the sleeve portions of the fork legs. Because the brake mechanism has to be a constant distance from the wheel axle, the sleeve portions are necessarily attached to the wheel axle with the rod attached to the steering tube and handle.
There are several disadvantages of this arrangement, the most notable of which is the provision of the weakest component of the system at the area encountering the most stress. The greater stress is at the top of the fork legs encountered by the rods which are less resistant to bending. Also, the heaviest portion of the fork is attached to the wheel, slowing its response to and recovery from bumps. Furthermore, whereas it is desirable to contain the biasing members inside the sleeve portions of the fork legs, the interior of the sleeve portions are inaccessible other than by dismantling the fork from the front wheel.
Examples of prior shock absorbing systems available for mountain bike front wheels are disclosed in a February 1991 article of a biking magazine titled "Mountain Bike Action". At pages 75-78 of the magazine, comparisons are made between seven bikes equipped with front wheel shock absorbers. Five of the seven are as described above. A sixth uses the steering shaft or stem to absorb the shock and is not applicable. The final version uses the fork legs as the shock absorbing members but with the rod attached to the wheel axle to obviate the concern for the weaker component absorbing the greatest stress. It is referred to as the upside down fork and overcomes the problem of the brake attachment by providing a disc brake that acts against the wheel hub rather than the rim. The disc brake is unacceptable however since it is heavier and costs more to produce. As noted in the article;
"The reason that [the manufacturer] are the only upside-down forks on the market is the fact that upside-down forks require disc brakes. ([The Manufacturer] makes its own disc)".